1. Field of the Invention
The present invention generally relates to power control methods and circuits and power supply units, and more particularly to a power control method and circuit and a power supply unit which can set a rated output.
Electronic equipments such as portable or lap-top personal computers are designed so that it is possible to use a power supply unit such as an A.C. adapter as its power supply. The power supply unit is designed to satisfy a specification as a power supply, so that it is possible to supply a maximum power required by the electronic equipment.
Generally, the power supply unit such as the A.C. adapter supplies a predetermined output voltage and a predetermined output current, which are referred to as an rated output. The power supply unit guarantees that a serviceable life of the power supply unit, a temperature rise of the power supply unit and the like are within predetermined tolerable ranges even if the power supply unit is continuously used at the rated output.
2. Description of the Related Art
In the power supply unit such as the A.C. adapter, restrictions are introduced with respect to the size, cost and the like of the power supply unit, due to the need to guarantee continuous operation at the rated output. When continuously operating the power supply unit at the rated output, the temperature rise of the power supply unit caused by the heat generated from a power supply circuit within the power supply unit in particular becomes a problem.
On the other hand, when the operation of the electronic equipment such as the portable or lap-top personal computer is studied, a continuous operation at the rated output actually does not occur. For example, circuits within the portable or lap-top personal computer are made up of various circuit elements, but not all of these circuit elements operate constantly. The operation of the portable or lap-top personal computer is dependent upon the application program which is activated, and the circuits which operate within the lap-top personal computer differ from time to time depending on the application program which runs.
When the portable or lap-top personal computer is using its communication function such as connection to the internet and computer-to-computer communication, circuits related to a modem which connects the portable or lap-top personal computer to the telephone line operate, but the circuits related to the modem do not operate when the communication function is not used. Similarly, when the portable or lap-top personal computer is reading an application program or is reading or writing data by executing a program, circuits related to carrying out read and write with respect to a hard disk drive operate, but the circuits related to carrying out the read and write with respect to the hard disk drive do not operate when the program is carrying out numerical computations or is waiting for an input from an operator of the portable or lap-top personal computer.
Accordingly, a power consumption of the portable or lap-top personal computer changes every moment depending on the operation of the program, and compared to a maximum power consumption, an average power consumption of the portable or lap-top personal computer is considerably low. The average power consumption is on the order of approximately one-half the maximum power consumption.
In order to reduce the size, weight and cost of the A.C. adapter, for example, it is conceivable to define the rated power under which the A.C. adapter can continuously operate depending on the actual state of the power consumption of the portable or lap-top personal computer, as the rated output according to the specification of the A.C. adapter, so that it is possible to obtain from the A.C. adapter a power greater than the rated output for an extremely limited short time. However, when the A.C. adapter is constructed so that it is possible to obtain the power greater than the rated output, the time for which the power greater than the rated output is used cannot be limited by the design of the portable or lap-top personal computer which uses the A.C. adapter. In other words, the power used by the portable or lap-top personal computer depends greatly on the operating application program and the manner in which the portable or lap-top personal computer is used. As a result, it is virtually impossible to guarantee that the time for which the power greater than the rated output is used will be limited to an extremely short time. In addition, in a case where the portable or lap-top personal computer uses an A.C. adapter of a type different from the A.C. adapter which is originally designed for use with the portable or lap-top personal computer, it is impossible to limit the time for which the power greater than the rated output is used to the extremely short time.
No problem occurs even if the A.C. adapter is used at the rated output for a long period of time. However, when the A.C. adapter is used at the power greater than the rated output for a long period of time, the A.C. adapter abnormally generates heat due to the heat generated from the power supply circuit within the A.C. adapter. When the A.C. adapter abnormally generates heat, the A.C. adapter may break down or, the A.C. adapter may operate erroneously and cause the portable or lap-top personal computer which uses this A.C. adapter to operate erroneously or fail. In a worst case, the A.C. adapter may cause fire due to extreme heat. Therefore, even though it is possible to reduce the size, weight and cost of the A.C. adapter by the conceivable method described above, it is impossible to guarantee stable and sage operation of the A.C. adapter. Furthermore, the conceivable method is not practical in that the protection of the portable or lap-top personal computer which uses the A.C. adapter becomes insufficient.
According to the conventional power control method, the maximum power consumption of the electrical equipment which uses the power supply unit is obtained, by taking the above described problems into consideration, and the rated output of the power supply unit is set so that the power supply circuit within the power supply unit will not abnormally generate heat or break down even if the electronic equipment operates continuously for a long period of time at the maximum power consumption. This kind of power supply unit uses a switching regulator.
However, when the power supply unit is designed by taking into consideration the maximum power consumption of the electronic equipment, there is a problem in that it is difficult to reduce the size, weight and cost of the power supply unit. In addition, there is another problem in that it is impossible to guarantee the stable and safe operation of the power supply unit. Furthermore, there is still another problem in that it is impossible to sufficiently protect the electronic equipment which uses the power supply unit.
Accordingly, it is a general object of the present invention to provide a novel and useful power control method and circuit and power supply unit, in which the problems described above are eliminated.
Another and more specific object of the present invention to provide a power control method and circuit and a power supply unit, which can reduce the size, weight and cost of the power supply unit, guarantee stable and sage operation of the power supply unit, and sufficiently protect an electronic equipment which uses the power supply unit.
Still another object of the present invention is to provide a power control method for controlling an output of a power supply comprising a setting step variably setting a maximum rated output based on a temperature. According to the power control method of the present invention, an overload state exceeding a rated output is tolerated within a tolerable time, and a maximum tolerable rated output is reduced if the overload state continues for a time exceeding the tolerable time, so that an abnormal temperature rise of a power supply circuit can be positively prevented using a relatively simple construction.
An input to the power supply may be an A.C. input or a D.C. input, and the power control method may further comprise a converting step converting the A.C. or D.C. input to a D.C. output different from said input. In this case, it is possible to realize an A.C. adapter or a D.C. adapter which is compact and inexpensive, and also guarantee stable and safe operation.
A further object of the present invention is to provide a power control circuit for controlling an output of a power supply, comprising a setting section variably setting a maximum rated output based on input temperature information. According to the power control circuit of the present invention an overload state exceeding a rated output is tolerated within a tolerable time, and a maximum tolerable rated output is reduced if the overload state continues for a time exceeding the tolerable time, so that an abnormal temperature rise of a power supply circuit can be positively prevented using a relatively simple construction.
Another object of the present invention is to provide a power supply unit which converts an A.C. or D.C. input from a power supply to a D.C. output different from said input, comprising a power control circuit variably setting a maximum rated output based on input temperature information. According to the power supply unit of the present invention, an overload state exceeding a rated output is tolerated within a tolerable time, and a maximum tolerable rated output is reduced if the overload state continues for a time exceeding the tolerable time, so that an abnormal temperature rise of a power supply circuit can be positively prevented using a relatively simple construction.
Other objects and further features of the present invention may be apparent from the following detailed description when read in conjunction with the accompanying drawings.